Fix hanging on browser shutdown.

It seems that |gconf_client_*| API should be called exactly from the main thread
(which is UI thread), for example see https://bugzilla.mozilla.org/show_bug.cgi?id=518244

This CL partially reverts CL https://codereview.chromium.org/1640273002
and makes calls to |gconf_client_*| API at the main thread.

BUG=486077

Review-Url: https://codereview.chromium.org/1990453002
Cr-Commit-Position: refs/heads/master@{#394372}
2 files changed